The present invention relates to new optically active liquid crystal compounds, and liquid crystal compositions containing the said compounds, more particularly, the present invention relates to fluoroalkoxydiphenyl pyrimidines which are compounds having optically active groups, liquid crystal compositions containing the said compounds and electrooptic elements using the said compositions.
Liquid crystal display elements are widely used as various display elements, such as watches, electronic calculators, television sets, computer ends, etc., because these elements have excellent characters, such as operativity at low voltage, minimized consumption of electric power, obtainability of thin display elements and so on.
At present, display elements of a twisted nematic (TN) type are widely used as liquid crystal display elements. However, the response of the display element is slower than that of a display element of light emitting type such as an electroluminescent display, a plasma display, and the like. Although improvement of the response time of the liquid crystal display has been tried in many ways, it shows no sign of marked improvement.
However, a new display method using a ferroelectric liquid crystal that has been studied has a hope for the improvement of the response speed. (Clark et al, Appl. Phys. Lett. 36, 898 (1980)). This method utilizes a ferroelectric chiral smectic C phase (abbreviated as S.sub.c * phase hereinafter) or other smectic phase such as a chiral smectic F, G, H or I phase and the like. This method is realizes a quick response time less than 1/100 to 1/1000 of that of the TN display method and a memory effect of bistability. It is expected to have wide application in a large sized television set of dynamic picture display, a high-speed light shutter, and the like.
However, in spite of these excellent characteristics, already-known compounds do not show a very quick response. The reason is that a compound having a high value of spontaneous polarization in the ferroelectric liquid crystal phase is unknown. The spontaneous polarization is proportional to the response speed. It is known that the high value of spontaneous polarization is important to obtain the quick response. Compounds having a high value of spontaneous polarization have not been found.
Hitherto, as ferroelectric liquid crystal compounds having a central group represented by the following formula: ##STR3## the following types are reported. ##STR4## wherein S.sub.Y and S.sub.X are described as other smectic phases in Japanese Unexamined Publication No. 61-215373/1986. ##STR5## wherein S.sub.Y and S.sub.X are described as other smectic phases in Japanese Unexamined Publication No. 61-215373/1986. ##STR6## wherein S.sub.X is described as another smectic phase in Japanese Unexamined Publication No. 61-215374/1986. ##STR7## wherein when m is 1, n is 5 and when m is 6, n is 1, etc., in Lecture Collection of the thirteenth meeting of liquid crystal discussion 1Z03, page 46.
Furthermore, the following compounds are described in the specification which was filed by the inventors of the present invention. (Japanese Patent Application No. 62-262819/1987). ##STR8##
In the compounds described in the above Japanese Unexamined Publication Nos. 61-215373 and 61-215374/1986, and Lecture Collection of the thirteenth meeting of liquid crystal discussion 1Z03, the spontaneous polarization (P.sub.S) which is an important physical property value of ferroelectric liquid crystals is very small. Moreover, the compounds described in the above Japanese Patent Application No. 62-262819 are difficult to show liquid crystal phases.